Because Jawook is a pampered baby, he wants a beautiful and tender love, he's not a freaking sub, Gyeon!!!
Anyway, this was so pleasurable for Gyeon? I thought he'd need something way more hardcore so I'm relieved (lol), but also idk why the author tried to make him the BDSM's master when it's obvious that yeah, he's hella twisted/obsessive (his last lines in this chapter, omg), but he also enjoys it cute. Idk if it was truly necessary to create this whole vibe of the darkest guy who's unreachable and impossible to satisfy (because this is the vibe that I'm getting of how others see him) that suddenly one day falls for a cute puppy and changes everything.
Tbh idk if u can learn to enjoy being a sub (the role) with no inner material for that, I mean, IMO Jawook is already pretty submissive (but aside from that the author hasn't shown more) and the most important thing for him is to give pleasure to his partner, so in theory, now that he's seeing Gyeon truly enjoying something and doing his stuff, maybe he'll feel pleasure as well? Maybe that was the key? Not having relationships like machines but with someone who truly enjoys being with u? I hope so, honestly, their relationship worries me, haha.